1. Field of the Invention
The invention is directed to methods and systems of hyperspectral and multispectral imaging of biological and medical tissues. In particular, the invention is directed to new devices, tools and processes for the detection and evaluation of diseases and disorders such as diabetes and peripheral vascular disease that are amenable to diagnosis using hyperspectral/multispectral imaging.
2. Background of the Invention
Diabetes afflicts an estimated 194 million people worldwide, affecting 7.9% of Americans (over 21 million people) and 7.8% of Europeans. Between 85% and 95% of all diabetics suffer from Type 2 diabetes, although nearly 5 million people worldwide suffer from Type 1 diabetes, affecting an estimated 1.27 million people in Europe and another 1.04 million people in the United States. Both Type 1 and Type 2 diabetic patients are at higher risk for a wide array of complications including heart disease, kidney disease (e.g. nephropathy), ocular diseases (e.g. glaucoma), and neuropathy and nerve damages to name a few2. The feet of diabetic patients are at risk for a wide array of complications, which are discussed below. Problems with the foot that affect the ambulatory nature of the patient are not only important from the standpoint of physical risk, but also convey an emotional risk as well, as these problems disrupt the fundamental independence of the patient by limiting his or her ability to walk.
Peripheral arterial disease (PAD) affects primarily people older than 55. There are currently 59.3 million Americans older than 55, and over 12 million of them have symptomatic peripheral vascular disease. It is estimated that only 20% of all patients with PAD have been diagnosed at this time. This represents a dramatically underpenetrated market. Although pharmacologic treatments for PAD have traditionally been poor, 2.1 million nevertheless receive pharmacologic treatment for the symptoms of PAD, and current diagnostic tests are not considered to be very sensitive indicators of disease progression or response to therapy. Additionally, 443,000 patients undergo vascular procedures such as peripheral arterial bypass surgery (100,000) or peripheral angioplasty (343,000) annually and are candidates for pre and post surgical testing. One difficulty in diagnosing PAD is that in the general population, only about 10% of persons with PAD experience classic symptoms of intermittent claudication. About 40% of patients do not complain of leg pain, while the remaining 50% have leg symptoms which differ from classic claudication.
Relying on medical history and physical examination alone is unsatisfactory. In one study, 44 percent of PAD diagnoses were false positive and 19 percent were false negative when medical history and physical examination alone were used.3 For this reason, physicians have looked for other means to help in providing diagnosis. As in the case of diabetic foot disease, current technologies have fallen short. Nonetheless, patients are frequently sent to peripheral vascular laboratories for non-invasive studies. While the test results are known to be inaccurate, these results do provide some additional information to physicians for assistance in diagnosis or treatment decisions.
Another problem faced by physicians is disease of the peripheral veins. Venous occlusive disease due to incompetent valves in veins designed to prevent backflow and deep vein thrombosis results in venous congestion and eventually stasis ulcers. Approximately 70% of leg ulcers are due to venous occlusion. Many of these ulcers are found at the medial malleolus. The foot is generally swollen and the skin near the ulcer site is brownish in appearance.
Pathology
Diabetic feet are at risk for a wide range of pathologies, including microcirculatory changes, peripheral vascular disease, ulceration, infection, deep tissue destruction and metabolic complications. The development of an ulcer in the diabetic foot is commonly a result of a break in the barrier between the dermis of the skin and the subcutaneous fat that cushions the foot during ambulation. This, in turn, can lead to increased pressure on the dermis, resulting in tissue ischemia and eventual death, and ultimately result in an ulcer.4 There are a number of factors that weigh heavily in the process of ulceration5-affecting different aspects of the foot—that lead to a combination of effects that greatly increase the risk of ulceration:6                 Neuropathy—Results in a loss of protective sensation in the foot, exposing patients to undue, sudden or repetitive stress. Can cause a lack of awareness of damage to the foot as it be occurs and physical defects and deformities7 which lead to even greater physical stresses on the foot. It can also lead to increased risk of cracking and the development of fissures in calluses, creating a potential entry for bacteria and increased risk of infection.8         Microcirculatory Changes—Often seen in association with hyperglycemic damage.9 Functional abnormalities occur at several levels, including hyaline basement membrane thickening and capillary leakage. On a histologic level, it is well known that diabetes causes a thickening of the endothelial basement membrane which in turn may lead to impaired endothelial cell function.        Musculoskeletal Abnormalities—Include altered foot mechanics, limited joint mobility, and bony deformities, and can lead to harmful changes in biomechanics and gait. This increases pressures associated with various regions of the foot. Alteration or atrophy of fat pads from increased pressure can lead to skin loss or callus, both of which increase the risk of ulceration by two orders of magnitude.        Peripheral Vascular Disease—Caused by atherosclerotic obstruction of large vessels resulting in arterial insufficiency10 is common in the elderly populations and is yet more common and severe in diabetics.11 Diabetics may develop atherosclerotic disease of large-sized and medium-sized arteries, however, significant atherosclerotic disease of the infrapopliteal segments is particularly common. The reason for this is thought to result from a number of metabolic abnormalities in diabetics, including high LDL and VLDL levels, elevated plasma von Willebrand factor, inhibition of prostacyclin synthesis, elevated plasma fibrinogen levels, and increased platelet adhesiveness.        Venous Disease—Caused by incompetent valves controlling backflow between the deep veins and the more superficial veins or thrombosis of the deep veins. Venous occlusions are typically observed in the elderly who typically presented with swollen lower extremities and foot ulcers typically at the medial malleolus.        
Previous studies have shown that a foot ulcer precedes roughly 85% of all lower extremity amputations in diabetic patients12, 13 and that 15% of all diabetic patients will develop a foot ulcer during the course of their lifetimes.14 More than 88,000 amputations performed annually on diabetics,15 and roughly an additional 30,000 amputations are performed on nondiabetics, mostly related to peripheral vascular disease. Estimations have shown that between 2-6% of diabetic patients will develop a foot ulcer every year13, 16 and that the attributable cost for an adult male between 40 and 65 years old is over $27,000 (1995 US dollars) for the two years after diagnosis of the foot ulcer.16 In conjunction with the increased total costs of care, Ramsey et al showed that diabetic patients incurred more visits to the emergency room (more than twice as many as control patients), more outpatient hospital visits (between 2× and 3× as many as control subjects) and more inpatient hospital days (between 3× and 4× as many as control patients) during the course of an average year.
Foot pathology is major source of morbidity among diabetics and is a leading cause of hospitalization. The infected and/or ischemic diabetic foot ulcer accounts for about 25% of all hospital days among people with diabetes, and the costs of foot disorder diagnosis and management are estimated at several billion dollars annually.16, 17 
Current Diagnostic Procedures
The first step in the assessment of the diabetic foot is the clinical examination18, 19. All patients with diabetes require a thorough pedal examination at least once a year, even without signs of neuropathy. Evaluation of the diabetic patient with peripheral vascular disease should include a thorough medical history, vascular history, physical examination, neurologic evaluation for neuropathy and a thorough vascular examination.20 
The next step in the work up of a patient with significant peripheral vascular or diabetic foot disease is non-invasive testing.21 Current clinical practice can include ankle brachial index (ABI), transcutaneous oxygen measurements (TcPO2), pulse volume recordings (PVR) and laser Doppler flowmetry. All of these clinical assessments are highly subjective with significant inter- and intra-observer variability especially in longitudinal studies. None of these methods are discriminatory for feet at risk, and none of them provide any information about the spatial variability across the foot. Doppler ultrasound with B-mode realtime imaging is typically used to diagnose deep vein thrombosis while photo and air plethysmography are used to measure volume refill rates as a means of locating and diagnosing valvular insufficiency. Currently there is no method to accurately assess the predisposition to serious foot complications, to define the real extent of disease or to track the efficacy of therapeutics over time.